1. Field of the Invention
This invention relates to an apparatus for steering or otherwise guiding a payload through the inside of a substantially horizontal pipe. More particularly, this invention relates to an apparatus for transporting instrumentation or other equipment for internal inspection, maintenance and/or repair of an underground pipe, such as a utility pipeline, which apparatus automatically maintains a functional orientation within the pipe as it moves through the pipe. Typically, the payload is mounted to a support that is pulled or pushed or otherwise motivated along the centerline of the pipe.
2. Description of Related Art
Internal inspection, maintenance and repair of underground utility pipelines is frequently utilized to avoid expensive excavation of the ground surrounding the pipeline. In addition to being expensive, excavation offers the potential for damage to the pipeline resulting, for example, from contact with the excavation equipment.
Tools for internal pipeline inspection perform a wide variety of specific functions, such as geometric surveys, determination of metal loss, and detection of cracks or leaks. Conventional means for transporting such payloads through the inside of the pipeline have a tendency to tip or otherwise spiral within the pipeline as they travel along the pipeline. To provide the accuracy required for internal pipeline inspection, it is important to be able to maintain a fixed radial orientation while traveling through the pipe. Any imbalance in the conveyance apparatus seen by the payload can cause it to ride up the pipe wall. This, in turn, can cause the payload carriage to spiral as it moves through the pipe and, in some instances, may even cause the payload carriage to become immobilized if it flips over. Generally, this spiraling may be avoided by ensuring that the payload carriage follows the “valley” or lowest point of the pipe interior as it travels through the pipe.
Going forward, internal pipe crawlers will need to be smaller in order to navigate sharp turns and pass through narrow launch tubes. The minimum number of pipe tracking contactors, e.g. wheels or tires, that can utilize opposing pipe walls sections, instead of gravity like a car on a flat road, is two. Accordingly, future needs to locate, inspect, and repair pipelines will best be served by pipe crawlers that have at least one pair (and preferably only one pair) of contactors and can maintain their orientation while traveling along the inside of the pipe.
Pipe crawlers currently in use employ a passive orientation within a pipe, i.e., they either sit at the bottom of the pipe or they are shaped with three sets of wheels distributed in a triangle. Whether powered or not, they maintain their alignment inside the pipe because of their shapes.
To maintain traction inside a pipe, a two-wheel pipe crawler must keep both wheels or tires or other form of rollable pipe contactor, such as a ball, in contact with the pipe wall. In an upright or vertical orientation, this means staying upright and not falling forward or backward. In a horizontal orientation, this means staying centered along the major pipe diameter and not dropping to the pipe bottom after skewing.
U.S. Pat. No. 7,343,863, (the '863 patent) which is incorporated by reference herein in its entirety, teaches an apparatus for transporting a payload inside a pipeline which addresses the problem of spiraling of the apparatus within a pipe. The apparatus comprises vertically aligned upper and lower roller elements which are relationally pivotably connected with each other and which contact the inside surface of the pipe into which the apparatus is inserted. The apparatus further comprises a steering pendulum which enables the apparatus to maintain a substantially vertical orientation as it is pushed or pulled through the pipe. However, operation of the apparatus requires the use of two apparatus units connected together, a front apparatus unit and a back apparatus unit, to avoid forward or backward tipping of the apparatus.